1. Field of the Invention
Example embodiments generally relate to a recording medium conveyer, and more particularly, to a recording medium conveyer for conveying a recording medium, for example.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium (e.g., a sheet) according to image data. Thus, for example, an image forming device forms an image according to the image data. A recording medium conveyer then sends a sheet from a paper tray toward an image transfer portion at which the image formed by the image forming device is transferred onto the sheet. In the recording medium conveyer, a separator including a feed roller and a separation pad separates an uppermost sheet from other sheets loaded in the paper tray by friction and feeds the uppermost sheet toward a registration roller pair. The registration roller pair feeds the sheet toward the image transfer portion.
In such image forming apparatus, friction applied to the sheet by the feed roller and the separation pad to forward the sheet may skew the sheet as it moves. Consequently, the sheet may be jammed in the image forming apparatus or the image may not be transferred at the proper position on the sheet. In order to correct such skew of the sheet, the sheet is contacted and stopped by the registration roller pair so that the sheet is bent between a nip portion formed between the feed roller and the separation pad and a nip portion formed by the registration roller pair.
In one example recording medium conveyer, an intermediate conveying roller pair is provided between the feed roller and the registration roller pair. After a sheet fed by the feed roller is bent when contacted and stopped by the registration roller pair, the registration roller pair starts rotating and the intermediate conveying roller stops rotating. The rotating registration roller pair rotates the intermediate conveying roller via the sheet to apply tension backward to the sheet, so as to correct skew of the sheet and prevent creasing of the sheet.
Increasing demand for more compact image forming apparatuses requires omission of the intermediate conveying roller pair and location of the paper tray directly under the image forming device. Accordingly, the sheet fed by the feed roller turns substantially before reaching the registration roller pair. Further, a sufficient space for absorbing bending of the sheet may not be provided. Consequently, skew of the sheet may not be corrected or the sheet nipped and bent between the nip portion formed between the feed roller and the separation pad and the nip portion formed by the registration roller pair may be twisted. When the sheet is thin paper, the twisted sheet may be creased.
On the other hand, in order to handle different types of sheets of varying thicknesses, such as thin paper and thick paper, another example image forming apparatus includes one motor for driving the feed roller and another, separate motor for driving the registration roller pair. This arrangement controls the feed roller so that the feed roller rotates at a speed faster than a speed of the registration roller pair, or continues driving the feed roller after driving the registration roller pair.
Although the above-described configuration can accommodate different types of sheets of varying thicknesses, it is known that a thin sheet is conveyed at a speed faster than a speed at which a thick sheet is conveyed because the thin sheet and the thick sheet have different slip rates of the sheet slipping on the feed roller. Accordingly, the thin sheet may be bent substantially between the nip portion formed between the feed roller and the separation pad and the nip portion formed by the registration roller pair. Consequently, the thin sheet may be twisted and creased or skew of the thin sheet may not be corrected.